Von Recklinghausen neurofibromatosis (NF1) is a common autosomal dominant disorder characterized by abnormalities in multiple tissues derived from the embryonic neural crest. The NF1 gene has been mapped to the pericentromeric region of the long arm of chromosome 17. Chromosome walking and sequencing of the NF1 gene have extended it's open reading frame; to date 49 exons have been identified. To investigate the mutation of the NF1 gene, the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method was applied to 4 exons of NF1 genes. We examined the DNAs from 49 samples, including those of 23 Japanese patients with NF1 (4 of these patients developed malignant schwannoma), a patient with segmental neurofibromatosis, and 14 clinically normal controls. A mutational band was detected in an exon of a tumor DNA extracted from a malignant schwannoma of a female NF1 patient. However, the mutation was not found in the germ line DNA of this patient. No mutations were detected in the other samples.